Gas supply apparatus and method for the supply of treatment gas to a person or to an animal

ABSTRACT

A gas supply apparatus for supplying anesthetic to a human or animal. A vaporizer has a vaporization chamber which includes a gas inlet and outlet. A liquid emitting device in the vaporization chamber communicates with an external liquid source through a liquid delivery. The liquid to be vaporized is exposed to the bypassing gas by way of the liquid emitting device. The liquid is exposed exclusively by way of the porosities in the liquid emitting device. A heater is provided for heating said liquid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/SE 98/00633, filed Apr. 6,1998.

The present invention relates to an apparatus and method for supplyingtreatment gas, e.g., an anaesthetic, to a human being or to an animal.

FIELD OF INVENTION

Although the invention can be applied in a number of differentapplications in respect of supplying treatment gas to human beings andto animals, it finds particularly beneficial use in the anaesthesia ofpatients, in which case it is intended that the apparatus is connectedto the system of hoses and devices by means of which breathing gas issupplied to a patient and to deliver the anaesthetic in a gasified stateto the patient concerned.

DISCUSSION OF THE BACKGROUND

Anaesthetic vaporisers are well known to the art, and a large number ofdifferent methods have been described. With regard to known and usedvaporisers, reference is made to Anaesthetic Equipment, C. S. Ward,published by Bailliere Tindall, 2nd edition, 1987, pp. 78-103 and toAnaesthesia Vaporisers by J. B. Eisenkraft in Anaesthesia Equipment,Principles and Applications, by Jan Ekrenwerth, James B. Eisenkraft,published by Mosby, 1993, pp. 57-58.

The earlier described vaporisers are based on the principle of storingliquid anaesthetic in a container into which there is introduced abreathing gas which passes over the liquid surface or bubbles throughthe liquid anaesthetic.

During this passage of the breathing gas, part of the anaesthetic isvaporised and entrained by the breathing gas to the patient. Thismethod, however, is encumbered with a large number of problems.

1. As the anaesthetic is vaporised, energy is taken from the liquefiedgas, which is therewith cooled. This cooling can result in a change inthe vapour pressure above the surface of the liquid and therewith alsochange the amount of anaesthetic that is entrained by the breathing gas.

This problem has been dealt with by delivering additional heat in thecase of some designs, or by varying the amount of breathing gas thatpasses over the liquid surface and then combining different gas flows soas to enable a constant anaesthetic content to be obtained in thebreathing gas.

2. Vaporisation of the anaesthetic is dependent on the rate of flow ofthe breathing gas. Attempts to compensate for this dependency have beenmade by using different intricate flow-dependent valves and gas mixingsystems in the vaporiser. The flow dependency can become problematic,particularly in the case of low fresh-gas flows that are used inso-called low flow systems.

3. Different anaesthetics have different vaporisation characteristicsand need to be used in different concentrations for optimum anaesthesia.Attempts to compensate for this have been made by designing vaporisersthat are each adapted for use with solely one anaesthetic. One drawbackwith this resides in the risk of filling a vaporiser with the wronganaesthetic, i.e. with an anaesthetic for which it is not intended. Thiswould have a catastrophic effect. The need for several differentvaporisers to be mounted together on a single anaesthetic apparatus alsoinvolves the risk of all vaporisers being in operation simultaneously,with the accompanying risk of administering an anaesthetic overdose.

4. Anaesthetics have different vaporisation characteristics in differentgas mixtures. This can result in administering to a patient a differentamount of anaesthetic than that for which the vaporiser is set, due tothe composition of the gas mixture.

5. A number of systems are based on the immersion of a wick in theanaesthetic. The anaesthetic is drawn up by the wick and vaporised onits surface. The drawback with this system, however, is that the rate atwhich the anaesthetic is drawn up the wick will depend on the height andtemperature of the liquid surface, therewith necessitating the inclusionof a compensatory system in the vaporiser.

DE-A 4 105 163 teaches a anaesthetic vaporising system in which a porousbody throughpassed by anaesthetic gases is saturated with anaesthetic.

The drawback with this system is that the amount of anaesthetic thatshall be used is restricted by the absorbency of said body, and thatevaporation of the anaesthetic in the passing gas will vary with time,due to lowering of the temperature of said body (due to evaporation ofthe gas). This means that a separate temperature control circuit must beprovided in order for the system to function satisfactorily. There is nopump or active means for supplying liquefied gaseous anaesthetic to theabsorption-desorption material.

U.S. Pat. No. 4,015,599 describes that the absorbent keeps anaestheticin a two-dimensional state (it is not disclosed what is actually meantby this). The anaesthetic is kept in a liquid state by means of a wick.This system also utilises a pre-charged absorbent bed through whichgases pass. The drawback with this system is that it also requires theuse of a temperature control means and that differentevaporation-absorption rates are obtained with different anaestheticgases.

U.S. Pat. No. 3,540,445 describes a vaporiser in which fibrous wickshave been replaced with porous synthetic plastics that absorb theanaesthetic from a container through the medium of capillary forces.Although the container can admittedly be topped-up, the amount ofanaesthetic taken up by the passing gas is primarily determined by theevaporation from the porous plastic rods and the capillary forces withinthese rods (when the level in a vessel filled with anaesthetic is keptconstant), and consequently the apparatus becomes temperature-dependentand also dependent on the anaesthetic to be vaporised.

GB 2 255 912 describes a system that uses porous rods through which thegas passes on the one hand and which are passed by the gas on the otherhand. These rods are supplied with gaseous anaesthetic, by submergingthe rods in the anaesthetic. The level of anaesthetic in relation to therods is regulated by a level regulator. It is necessary to regulate therods and the temperature of the anaesthetic and the gas in order toobtain a stable concentration of anaesthetic in the gas.

GB 2 279 015 describes an apparatus in which the liquid to be vaporisedis exposed to the gas, partly through porosities and partly through thefree liquid surface, thereby also requiring the provision of temperaturecontrol means. The apparatus has no liquid quantity control facility.

SUMMARY OF THE INVENTION

The object of the present invention is to eliminate several of thedrawbacks of the aforedescribed systems and to provide a method andapparatus that will provide uniform vaporisation of a large number ofdifferent anaesthetics in respect of a large number of different gasmixtures and flows.

The present invention relates to a gas supply apparatus and method forsupplying a treatment gas, e.g., an anaesthetic, to a patient or animalusing a porous liquid-emitting device connected to a liquid supply meanswhich communicates with an external liquid source. The liquid to bevaporised is exposed exclusively to bypassing gas by way of theporosities in the liquid-emitting device.

The invention is thus based on delivering the liquid to be vaporisedactively to the liquid emitting device, and is not therefore encumberedby the drawbacks associated with the type of system in which thevaporiser is charged with an initial quantity of liquid which isconsumed during the process and the vaporisation process therebyinfluenced, i.e. such systems as those exemplified by the first threepatent publications mentioned above.

The invention is based on the same liquid delay principle as thatdescribed in the aforementioned publication GB 2 255 912, according towhich liquid is delivered constantly to the liquid emitting device froman external liquid source. However, those problems that accompany theconstruction of this apparatus with the inclusion of porous rods thatare partially immersed in a liquid and with the free liquid surface incontact with the bypassing gas, and where the vaporisation process inthe rods is sensitive to variations in liquid level have been avoided bymeans of the special features of the present invention. Thus, the liquidin the liquid emitting device is exposed solely through its porosities,so as to eliminate the effect of the level of a free liquid surface.Because the liquid is exposed solely via said porosities, the deliveryof vaporised medium is determined solely by the delivery rate of thepump. Furthermore, there is provided a large and constant exposuresurface area, so that the rate of evaporation will be at least equal tothe liquid-emitting rate and can also be controlled, regulated, in asure and purposeful manner.

The facility of enabling the liquid to be heated with the aid of theheating device enables the temperature of the liquid to be adapted inrelation to the nature of liquid to be vaporised, so as to obtainoptimum conditions with regard to the vaporisation process.

According to one preferred embodiment of the invention, the heatingdevice is placed within the liquid-emitting device, therewith providingeffective heating.

According to a second preferred embodiment, the heating device is placedoutside but adjacent to the liquid-emitting device, therewith enablingthe components to be arranged simply.

One quick and simple method of heating the liquid is to use a heatingdevice in the form of an electric resistance, this embodiment comprisinga further preferred embodiment of the invention.

According to another preferred embodiment, the liquid-emitting devicescan be controlled so as to adapt readily to variations in requirements,for instance in response to different types of liquid to be vaporised.

In yet another preferred embodiment of the invention, the liquid isdelivered by means of a pump, preferably a motor-driven pump, so as toprovide safe and uniform supply of liquid and to enable the liquidsupply to be readily regulated.

According to another preferred embodiment of the invention, theconcentration of vaporised liquid in the outgoing air is preferablysensed by an optical sensor which appropriately controls the regulationof the amount of liquid supplied.

The aforedescribed embodiments and other preferred embodiments of theinvention are set forth in the dependent claims.

The invention will now be described in more detail with reference topreferred embodiments of the invention and also with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a principle diagram illustrating an apparatus according to apreferred embodiment of the invention.

FIG. 1a is a sectional view taken on the line I—I in FIG. 1.

FIGS. 2-5 illustrate schematically various ways of connecting theinventive apparatus when using said apparatus in an anaesthesia system.

FIGS. 6-8, 6 a-8 a illustrate alternative embodiments in a mannercorresponding to FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The apparatus illustrated in FIG. 1 includes a vaporising chamber 1formed by a container 2. Although the container is shown to have atubular shape it will be understood that it may have any other desiredshape. The vaporisation chamber 1 has an inlet opening 3 which isconnected to a gas delivery inlet line, (not shown) as symbolised withthe arrow A, and an outlet opening 4 which is connected to a gasdischarge outlet line (not shown), symbolised with the arrow B. Theoutlet line is intended for connection with the respiratory organs of apatient for the delivery of, in this case, anaesthetic gas. Arranged inthe vaporisation chamber 1 is a liquid-emitting device 5 in the form ofa porous body. The porous body has a cylindrical shape and isconveniently made of plastic material. A delivery line 6 for thedelivery of anaesthetic in liquid form is connected to theliquid-emitting device 5.

As the gas flows from the inlet 3 and through the chamber 1 to theoutlet 4, it passes the liquid-emitting device 5 and comes into contactwith the liquid present in the porosities of said device. As the liquidis exposed to the bypassing gas, the liquid will be vaporised byevaporation. Fresh liquid is constantly delivered from the delivery line6 through the passageways formed by the inner porosities of the porousbody out to the surface-located porosities, such that the process willbe continuous in principle. The outflowing gas B will therewith containa certain amount of vaporised anaesthetic.

The liquid delivered from the delivery line 6 is led directly to theporosities in the liquid-emitting device 5. The delivery is thus activeand does not take place via a reservoir arranged in the proximity of theliquid-emitting device and from which liquid is drawn into theporosities via capillary action. This avoids the control problems anduniform flow problems that result from such capillary supply. Becausethe liquid is delivered directly to the porosities, the liquid will alsobe exposed to the gas exclusively via said porosities and not via a freeliquid surface. In the embodiment shown, liquid-emitting device 5 liesagainst the inner surface of the wall of the vaporisation chamber. Theinner surface of the wall includes grooves 13 which communicate with theliquid delivery line 6.

In the illustrated example, liquid anaesthetic is delivered from anexternal anaesthetic container 8 to the liquid-emitting device 5 throughthe medium of a pump 7.

Alternatively, the external container 8 can be positioned at a heightsufficient to deliver the liquid gravitationally. In the case of thisalternative embodiment, the pump 7 is replaced with a control valve.

A sensor 9 is mounted in the path of gas flow, downstream of theliquid-emitting device 5. The sensor may be an optical sensor thatsenses the optical absorption of the gas at different light wavelengths.Alternatively, the sensor may have a form of an opening connected to ahose for withdrawing a gas sample. The sensor 9 is coupled to a signalunit 10 which, via a signal line 11, sends signals to a control unit 12that controls the pump 7.

When an optical sensor is used, the signal unit 10 is comprised of asignal converter which, depending on the sensor reading, forwards arelevant signal to the control unit 12. When the sensor 9 has the formof a gas sampler, the signal unit 10 includes analysis instruments whichanalyse the gas content and send signals to the control unit 12 on thebasis of this analysis.

The control unit 12 may be an electric, electronic or electromechanicalunit, although a microprocessor controlled unit is preferred. Thecontrol unit influences the pump flow solely by varying the operationalresistance of the motor or by directly varying the operating state ofthe pump. The control unit 12 and the pump 7 may conveniently beincorporated as one single unit. The pump may be an injector pump.

The aforedescribed control apparatus is effective in controlling theamount of liquid anaesthetic delivered to the liquid-emitting device 5per unit of time on the basis of the concentration of anaesthetic in thedeparting gas B.

An electrical resistance 50 with connection lines 51, 52 is arrangedbetween the liquid-emitting device 5 and the wall of container 2. Theresistance 50 functions to heat the liquid present in theliquid-emitting device.

FIGS. 2 to 5 illustrate different ways of connecting the inventivevaporising apparatus in a system for delivering anaesthetic gas to apatient.

In the FIG. 2 embodiment, the gas flowing into the container 2 throughthe gas delivery line 29 is comprised of a mixture of fresh gas enteringfrom a line 15 and recycled gas entering from a line 14. Theanaesthetic-containing gas is led on the outlet side through the line 17to a line 19 leading to the patient, via a Y-coupling 18. The otherbranch of the Y-coupling 18 is comprised of the line 16 for exhalationgas.

The coupling shown in FIG. 3 is modified inasmuch that the container 2is connected between the Y-coupling 22 and the patient supply line 21.Reference numeral 24 identifies the inhalation hose, 26 identifies thefresh gas hose, reference 26 identifies the hose for re-circulated gas,and 23 identifies the exhalation hose.

In the FIG. 4 embodiment, the container 2 is arranged in the fresh gashose 31. In FIG. 3, the reference 32 identifies the patient supply hose,33 identifies the Y-coupling, 34 identifies the hose for re-circulatedgas, 35 identifies the exhalation hose, and 36 identifies the inhalationhose.

In the alternative shown in FIG. 5, the container 2 is placed in theexhalation hose 41. Reference 42 identifies the patient supply hose, 44identifies the inhalation hose, 45 identifies the fresh air hose, and 46identifies the hose for re-circulated gas. In the case of this coupling,the sensor 9 is placed separately from other components in thevaporising apparatus, although it is, of course, in signal communicationtherewith.

In the case of the FIG. 5 embodiment, the gas is enriched withanaesthetic in the exhalation hose 41, so that the recirculation hose 46will convey gaseous anaesthetic. That part of the exhalation hose 41located downstream of the container 2, the re-circulation hose 46, andthe inhalation hose 44 all form parts of the container outlet line.

The apparatus illustrated in FIGS. 6-8, 6 a-8 a exemplify modifiedembodiments of the liquid-emitting device 5, although these apparatusare, in general, identical with the embodiment according to FIGS. 1, 1a. In the embodiment according to FIGS. 6, 6 a, the body 5 has asegmental form, in FIGS. 7, 7 a a form which is elongated transverselyto the flow direction, and in FIGS. 8, 8 a a block-like form which isrounded to conform to the inner surface of the container 2. Asillustrated, the heating device 50 may be placed within theliquid-emitting device 5 in both of these latter embodiments.

What is claimed is:
 1. Gas supply apparatus for the supply of treatmentgas, e.g., an anaesthetic, to a human being or to an animal, wherein theapparatus has a vaporiser which includes a vaporising chamber that has agas inlet means and a gas outlet means and in which a porousliquid-emitting device is arranged to expose a liquid to said vaporisingchamber for vaporisation of liquid, and wherein the liquid-emittingdevice is connected to a liquid supply means which communicates with anexternal liquid source, and wherein the gas outlet means is adapted forconnection to an inhalation means, characterized in that saidliquid-emitting device lies against the inner surface of a wall of saidvaporising chamber and wherein said liquid supply means delivers saidliquid directly to said liquid-emitting device whereby the liquid isexposed exclusively via the porosities in the liquid-emitting device;and in that the apparatus includes liquid-heating means.
 2. Apparatusaccording to claim 1, wherein the heating means is adapted to heat theliquid present in the liquid-emitting device.
 3. Apparatus according toclaim 2, wherein the heating means is arranged within theliquid-emitting device.
 4. Apparatus according to claim 2, wherein theheating means is arranged externally of but adjacent to saidliquid-emitting device.
 5. Apparatus according to any one of claim 1,wherein the heating means is an electrical resistance.
 6. Apparatusaccording to any one of claim 1, wherein the liquid supply means isprovided with liquid-quantity control means.
 7. Apparatus according toany one of claim 1, wherein said liquid supply means includes a pump. 8.Apparatus according to claim 7, wherein the pump is motor-driven. 9.Apparatus according to claim 7, wherein the pump is a controllable pumpand therewith constitutes a component in said liquid-quantity controlmeans.
 10. Apparatus according to claim 8, wherein the apparatusincludes sensor means for sensing the vaporised liquid content, saidsensor means being located downstream of said liquid-emitting device.11. Apparatus according to claim 10, wherein said sensor means includesan optical sensor.
 12. Apparatus according to claim 10, wherein saidliquid-quantity control means is adapted to regulate the supply ofliquid in response to said sensor means.
 13. Apparatus in accordancewith claim 8, wherein said liquid-quantity control means is adapted todeliver per unit of time a quantity of liquid that is at most equal tothe quantity of liquid that is vaporised in said liquid-emitting deviceper unit of time.
 14. Apparatus according to claim 1, wherein saidliquid-emitting device is comprised of a plastic material.
 15. Apparatusaccording to claim 1, wherein the wall includes on the surface thereofthat lies against the liquid-emitting device grooves which communicatewith said liquid supply means.
 16. Apparatus according to claim 1,wherein the liquid-emitting device has the form of a hollow cylinder.17. A method of supply treatment gas to the respiratory organs of ahuman being or an animal, wherein liquid is delivered from an externalliquid source to a porous liquid-emitting device in which the liquid isexposed to a flowing gas so as to vaporise upon contact with said gas,whereafter the vapour is delivered to said respiratory organs, saidmethod comprising delivering said liquid directly to saidliquid-emitting device and exclusively exposing said liquid to said gasvia the porosities of said liquid-emitting device.
 18. A methodaccording to claim 17, wherein the liquid is heated when present in theliquid-emitting device; and in that heating is effected electrically.19. A method according to claim 18, wherein the supply of liquid isregulated.
 20. A method according to claim 17, wherein the liquid isdelivered with the aid of a motor-driven pump.
 21. A method according toclaim 17, wherein the gasified liquid content of the gas is sensed afterits contact with the liquid with the aid of an optical sensor; and inthat the amount of liquid delivered per unit of time is controlled onthe basis of this sensed content.